Hydraulic control system for electric lift truck

ABSTRACT

A hydraulic control system for a batter-powered electric lift truck includes hydraulically powered mast-tilting cylinders and fork hoist cylinders supplied with pressure fluid from an electric motor-driven small and large capacity pair of pumps. The hydraulic circuit supplying pressure fluid to the cylinders includes a pair of spool-type metering valves, one for the tilt cylinders and one for the hoist cylinder. The hoist spool is a three-position spool having a neutral position, a lowering position and a hoisting position range. When the spool is stroked through the hoist range from low to high, fluid is metered by the spool to the hoist cylinder first at a small flow rate and gradually at increasing rates only from the small pump until the maximum flow capacity of the small pump is reached. Thereafter, as stroking continues, flow from the large pump is added gradually and progressively to the maximum flow of the small pump until the full flow capacities of both pumps is utilized to extend the hoist cylinder. Thus through operator control of the hoist spool the hoist can be operated at either low or high speed and in small, slow increments for precise positioning. In the illustrated circuit, this progressive additive-metering of the flow from the small and large pumps occurs regardless of the position of the tilt spool. Both pumps, as well as the valve block housing the tilt and hoist spools, are enclosed within the hydraulic fluid reservoir for the system.

United States Patent 1 [111 ,754,394 Morrison [45] Aug. 28, 1973' HYDRAULIC CONTROL SYSTEM FOR tric lift truck includes hydraulically powered mast- ELECTRIC LIFT TRUCK [75] Inventor: Donald C. Morrison, Portland, Oreg.

[73] Assignee: Hyster Company, Portland, Oreg.

[22] Filed: Dec. 2, 1971 [211 Appl. No.: 204,106

52 US. Cl (so 482i, 6'0/5'2 US [51] Int. Cl. F1511 13/09 [58] Field of Search 60/52 HE, 52 US [56] References Cited UNITED STATES PATENTS 1,993,612 3/1935 Lum 60/52 US 2,103,530 12/1937 Henry 60/52 HE 2,979,908 8/1961 Shook 60/52 HE X 3,146,593 9/1964 Stacey 60/52 HE 3,203,183 8/1965 Lucien 60/52 US UX 3,338,441 8/1967 Flint 60/52 HE X 3,443,380 5/1969 Karazija 60/52 HE Primary Examiner-Edgar W Geoghegan V A ttorney-Stephen W. Blore,James S. Leigh et al.

tilting cylinders and fork hoist cylinders supplied with pressure fluid from an electric motor-driven small and large capacity pair of pumps. The hydraulic circuit supplying pressure fluid to the cylinders includes a pair of spool-type metering valves, one for the tilt cylinders and one for the hoist cylinder. The hoist spool is a three-position spool having a neutral position, a lowering position and a hoisting position range. When the spool is stroked through the hoist range from low to high, fluid is metered by the spool to the hoist cylinder first at a small flow rate and gradually at increasing rates only from the small pump until the maximum flow capacity of the small pump is reached. Thereafter, as stroking continues, flow from the large pump is added gradually and progressively to the maximum flow of the small pump until the full flow capacities of both pumps is utilized to extend the hoist cylinder. Thus through operator control of the hoist spool the hoist can be operated at either low or high speed and in small, slow increments for precise positioning. In the illustrated circuit, this progressive additive-metering of the flow from the small and large pumps occurs regardless of the position of the tilt spool. Both pumps, as well as the valve block housing the tilt and hoist spools, are enclosed within the hydraulic fluid reservoir for the system.

[57] ABSTRACT A hydraulic control system for a batter-powered elec- 22 Claims, 6 Drawing Figures lll-l. R 53251 HO|ST :N 36 i owra 2 I4 m 32 f 0 lli 0 f f F 1 7o 2 1n 'J ;JZ\ r71 \00\ qq 18 5a 73 3o 48 q+ n8 er 1 r-b- 5Z (V L- jJUl 1 41 50 5| l2 %4" 46x 78- m 80 r56 59 74 |o2 L 60 1 i 7, 1 we 5 8 I04 i 86* T -b 66 Q0 11 P l Ha I l Patented Aug. 28, 1973 3 Sheets-Sheet 1 SMALL PUMP PLUS LARGE PUMP BATTERY SPOOL STROKE Eli DONA L D C. MORRISON BY IN VE N TOR BUCKHORN, BLORE, KLAROUIST 8 SPARKMAN ATTORNEYS Patented Aug. 28, 1973 3,754,394

3 Sheets-Sheet 2 HOIST --HQ|ST "E 36 *POWER 20 32 BI 83 J67 f DONALD c. MORRISON BY INVENTOR BUCKHORN, BLORE, KLAROUIST 8 SPARKMAN ATTORNEYS Patented Aug. 28, 1973 3,754,394

3 Sheets-Sheet {5 DONALD C. MORRISON INVE N TOR BY BUCKHORN, BLORE, KLAROUIST 8 SPARKMAN ATTORNEYS HYDRAULIC CONTROL SYSTEM FOR ELECTRIC LIFT TRUCK BACKGROUND OF THE INVENTION I. Field of the Invention The present invention relates to a hydraulic control system for controlling the load-handling components of a battery-powered electric lift truck.

2. Description of the Prior Art Hydraulic systems utilizing two hydraulic pumps to power the load-handling components are common in the electric lift truck field.

One such prior system is shown, for example, in FIG. 2 of the Flint U. S. Pat. No. 3,338,441. However, in the Flint patent, the two pumps are provided in separate and independent hydraulic circuits, one supplying pressure fluid to the hoist cylinder and the other supplying pressure fluid to the tilt cylinders of the truck. Such a system tends to be inefficient because both pumps must have sufficient capacity to meet the maximum needs of the functions which they serve, since their flows cannot be combined, and thus both usually operate at only partial capacity. Furthermore, both pumps must operate under load at the same time if both tilt and hoist functions are to be operated simultaneously, even though the capacity of one pump might be adequate to supply the flow needs of both functions. Thus this system is also inefficient because it imposes high loads on the electric motor, which in turn drains power from the battery which might otherwise be used to drive the traction motor or other functions.

The Karazija U. S. Pat. No. 3,443,380 discloses another two-pump hydraulic system for an electric lift truck wherein both pumps supply pressure fluid to a common hydraulic circuit and spool valves in the circuit direct flow either to the tilt cylinders or alternatively to the hoist cylinder, but not to both at the same time. Separate electric motors are required to drive each pump. Only one pump and its motor are activated electrically, but at full speed, upon actuation of the tilt spool. The same pump and motor, or both pumps and motors, are activated electrically through actuation of the hoist spool, depending. on the positioning of such spool, to operate the hoist cylinder. However, this system, too, is inefficient since two electric motors are required. Also, both tilt and hoist functions cannot be operated at the same time. Furthermore, the hoist functions has only two speeds, fast and slow, with no provision for smooth transition between them, thereby tending to cause jerky operation and making precise vertical positioning of the load difficult. The Flint system has this same hoist control deficiency.

In an electric lift truck, the pumps are continuously driven at a high speed dictated by the speed versus load characteristics of the electric motor, regardless of the power or flow requirements of the hydraulic system. Thus in an electric lift truck, use of a single largecapacity pump is highly inefficient. Although the use of the two pumps in systems such as shown in the Flint and Karazija patents is a partial solution, it is not a complete solution because of the deficiencies of such systems as noted above.

There are also known hydraulic systems for vehicles which utilize both a small-capacity pump and a largecapacity pump, wherein the hydraulic load on the engine driving the pumps is automatically unloaded at a predetermined total engine load level to prevent the engine from stalling when high total loads are imposed on it. Such a system, driven by an internal combustion engine, is shown, for example, in the McAlvay U. S. Pat. No. 3,171,247. However, such a system is not suitable for electric lift trucks for which the hydraulic loadhandling functions of the vehicle should have priority over the traction function for practical aswell as safety considerations. Thus in a lift truck, it is most desirable to have a hydraulic system that is responsive primarily to hydraulic demand rather than to total available power including the power available to drive the vehicle.

In the prior Vickers U. S. Pat. No. 1,982,711, a hydraulic system is shown which uses both a largecapacity pump and a small capacity pump driven by a common motor for supplying pressure fluid to a hydraulic cylinder. The system is designed automatically to unload the large-capacity pump when high working pressures are developed and to cut in the full capacity of the large-capacity pump under low-pressure, highvolume circuit conditions. However, the Vickers system is a pressure-responsive system which would not be suitable for an electric lift truck application where it is desirable that the operator have full control of the flow available to drive the load-handling hydraulic functions.

SUMMARY OF THE INVENTION According to the present invention, a hydraulic control system for a battery-powered electric lift truck is provided which is a distinct improvement over prior such systems. In this regard, the system of the invention includes a small-capacity pump and a large-capacity pump driven by the same electric motor. A single operator-controlled metering valve controls the flow available from both pumps to operate the hoist cylinder. When only the tilt function need be operated, an operator-controlled tilt valve meters flow as required only from the small capacity pump to the tilt cylinder, while the full flow capacity of the large pump is shortcircuited to reservoir to unload such pump and minimize the load imposed on the electric motor and the vehicles battery. When the hoist function is operated, or when both the hoist and tilt functions are operated, flow is metered first only from the small-capacity pump to the hoist and tilt cylinders as required by the positions of the hoist and tilt valves until the full capacity of the small pump is utilized. Thereafter any additional flow requirements, as dictated by the position of the hoist valve, are supplied by flow from the largecapacity pump added to the maximum flow of the small pump, smoothly and progressively as required. Thus the large pump is loaded only when and to the extent required to supply demand flow to the hoist cylinder alone or to the hoist and tilt cylinders together, as dictated by the hoist and tilt valve positions. The foregoing features maximize the efficiency of the system by loading the electric pump motor and thus the vehicle battery only to the extent required to meet hydraulic needs, while at the same time providing excellent speed control and precise positioning control of the hoist function.

Thus a primary object of the invention is to provide a hydraulic control system for an electric lift'truck which is highly efficient in that it minimizes the load on the electric power system.

from the two pumps are controlled by a single opera- I tion controlled valve.

According to another important feature of the invention, both pumps of the system, as well as the valve block housing the hoist and tilt metering valves are enclosed within the reservoir for the hydraulic fluid of the system. This feature eliminates problems which might otherwise be caused by leakage of the hydraulic fluid from the valve block or pumps. These problems could be particularly acute in an electric lift truck where critical electrical circuits could be shorted out by such leakage. This feature furthermore reduces overall space requirements of the hydraulic system of electric trucks, in which space is always limited because of their small size.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying drawings wherein:

FIG. 1 is a schematic side elevation of a batterypowered electric lift truck showing the general arrange ment of major components of such truck;

FIG. 2 is a graph illustrating the operation of the control system of the invention in utilizing the flow capacities of pumps as a function of the stroke of a metering valve spool;

FIG. 3 is a hydraulic circuit diagram showing a hydraulic system of the invention in its neutral mode;

FIG. 4 is a diagram of the circuit of FIG. 3 showing the hydraulic system in a slow hoist mode;

FIG. 5 is a diagram of the hydraulic circuit of FIG. 3 showing the system in a fast hoist mode; and

FIG. 6 is a diagram of the circuit of FIG. 3 showing the system operating simultaneously in its hoistlowering and tilt-retracting modes.

DETAILED DESCRIPTION General Arrangement With reference to the drawings, FIG. 1 shows a battery-powered electric lift truck 10 with typical components, including a mast l2 pivoted at its lower end to the forward end of the lift truck and tiltable forwardly and rearwardly by hydraulic tilt cylinders 14. A load apron l6 movable vertically on the mast mounts a set of load-lifting forks 18 which move vertically with the apron under the influence ofa hoist cylinder 20. A battery assembly 22 is mounted within a rear portion of the truck and supplies electrical power for operating both a traction electric motor (not shown), and a second constant-speed electric motor 24. The latter motor drives a pair of fluid pumps for the truck's hydraulic system, including a small capacity pump 26 and a largecapacity pump 28. The pumps supply hydraulic fluid for operating the various load-handling components of the truck including tilt cylinders 14 and hoist cylinder 20.

The hydraulic system includes a hydraulic fluid circuit 30 shown schematically in FIGS. 3, 4, 5 and 6. Forming part of the hydraulic system is a valve block 32 housing a pair of operator-controlled spool valves, including a tilt cylinder control valve 34 and a hoist cylinder control valve 36. These valves are controlled remotely at the operators compartment 38 by control handles 40, 42 operatively connected either by mechanical or hydraulic means to the valve spools.

A unique feature of the hydraulic system is the enclosure of valve block 32 and the pumps 26, 28 entirely within the fluid reservoir 44 for the hydraulic fluid. This serves two basic purposes. First, it minimizes space requirements for the hydraulic system in the electric truck where space is always limited. Second, it prevents problems in the event hydraulic fluid should leak from either the valves or the pumps. Such leakage could be a particularly critical problem in an electric truck where electrical circuitry could be shortedout otherwise as a result of such leakage.

Now referring to FIGS. 3 through 6, the tilt valve spool 34 is a conventional spool-type metering valve having four lands, three grooves, and three positions. These include a neutral position shown in FIGS. 1, 2 and 3, a retract or rearward tilt position shown in FIG. 6, and an extend or forward tilt position (not shown) designated by the letter E.

However, hoist valve spool 36 is unique in its function and operation in the circuit. It includes five lands and four grooves, but still is basically only a threeposition spool valve, including a neutral position N, a lower position L and a hoist position between N and H. Thus the hoist" position is in reality a hoist metering range of positions extending from N at the lowspeed end to H at the high speed end.

Neutral Mode In the neutral positions of tilt spool 34 and hoist spool 36, shown in FIG. 3, pressure fluid flows from smallcapacity pump 26 through primary feed line 46 into tilt valve chamber 47, across tilt spool grooves 48, and into tilt valve chamber 49. From there flow is through line 50 into hoist valve chamber 51, across hoist spool grooves 52, into hoist valve chamber 53 and from there through line 54 to return line 56 and back to reservoir 44.

At the same time, the entire flow capacity of large pump 28 is unloaded to reservoir through feed line 58, into hoist valve chamber 59, across hoist spool groove 60, into hoist valve chamber 61, and from there through line 62 to return line 56.

Under such neutral condition of the circuit, both pump 26 and pump 28 are unloaded, whereby electric motor 24 operates at its constant speed with a minimum power drain from the battery.

Slow-Hoist Mode Referring to FIG. 4, tilt valve 34 is again shown in its neutral position, but hoist spool 36 is stroked slightly into the lower end of its hoist-metering range. In this position of the hoist spool, a portion of the flow capacity of pump 26 only is metered by spool 36 to hoist cylinder 20 to raise the cylinder at slowspeed. The remainder of the flow capacity of the small pump and all of the flow of the large pump are short circuited to reservoir. The circuit operates as follows: A portion of flow from pump 26 is again through line 46, through a line 64 and check valve 65 and through another line 66 bypassing tilt valve 34 to a line 67. Flow from line 67 is to a chamber 68 in the hoist valve, where flow continues across a small portion of hoist valve groove 69 into valve chamber 70 and from there through line 71 to the lower end of hoist cylinder 20. In the low-speed positions of the hoist-metering range of spool 36 only a portion of the flow from small-capacity pump 26 moves across the space between the hoist valve land 72 and the hoist valve body restriction 73. The remaining oil from small pump 26 is routed to dump through the metering notches 120 in hoist spool land 121, to hoist spool cavity 53, line 54 and return line 56 and back to reservoir 44.

Under the condition of the circuit shown in FIG. 4, the full flow of large-capacity pump 28 is again un loaded to reservoir through line 58, hoist valve chambers 59, 61, line 62, and line 56 in the same manner as described with respect to FIG. 3. However, it will be noted in FIG. 4 that hoist spool land 86 barely engages a hoist valve body restriction 87. Nevertheless, the flow of large-capacity pump 28 can flow from hoist valve chamber 59 into chamber 61 through metering notches 88 provided at the upper shoulder of land 86.

Fast-Hoist Mode Referring to FIG. 5, the hydraulic circuit is shown conditioned for fast-hoist operation. In this condition, tilt spool 34 is still in its neutral position, but hoist spool 36 is stroked upwardly so that it is at the upper end of its hoist-metering range. In this position of spool 36, the full flow of small pump 26 is directed through lines 46 and 64, through check valve 65, and around the tilt valve in line 66 to line 67. From line 67 the flow is to hoist valve chamber 68, across hoist valve body restriction 73 and spool groove 69, which now define a wide flow passage, and into line 71 leading to the hoist cylinder 20.

Under this condition, the metering notches 120 in spool land 121 are completely closed, requiring all flow from small pump 26 to be routed to the hoist cylinder 20. So long as the lifted load is within the capacity of the lift truck, there will not be sufficient pressure in line 46 to open pressure relief valve 74. Therefore normally none of the flow from pump 26 is diverted through line 76 back to the reservoir.

The flow path for the fluid from pump 26 as just described in FIG. 5 for the full-open, fast-hoist condition of spool valve 36 would also be the flow path followed by the fluid from the small pump 26 when the hoist spool is positioned about half-way between the fullopen position of FIG. 5 and the neutral position of FIG. 3. However, in the latter case, once again the full flow from the large-capacity pump would be diverted to sump in the manner shown in FIG. 4.

However, now in the full-stroke position of hoist spool 36, the flow capacity of the large pump 28 is also utilized to raise the hoist cylinder at a fast rate. Thus the flow from large pump 28, instead of going through line 58, which is now blocked by the hoist valve spool, is forced through check valve 90 in line 91 and into the primary feed line 46 where flow from the large pump follows the same flow path as just described with respect to the small pump. In other words, the full flow capacity of both pumps proceeds through line 46, around the tilt valve in line 66, and across the hoist valve body restriction 73 and spool groove 69 into line 71 directly to hoist cylinder 20.

Flow-Metering and Pump-Sequencing If the hoist valve is not in its full-stroke position shown in FIG. 5, but instead is stroked to a position near the upper end of its metering range, that is, somewhere between the position shown in FIG. 4 and that shown in FIG. 5, only part of the flow from the largecapacity pump would go through check valve in line 91 into primary feed line 46 and then to the hoist cylinder. The remainder of such large pump flow would be through line 58 and into hoist valve chamber 59, through notches 88 of hoist spool land 86, into chamber 61 and then through line 62 and return line 56 back to reservoir. However, the full flow of the small pump is still metered to the hoist cylinder as just described.

From the foregoing it will be apparent that the stroking of the hoist valve spool 36 from its neutral position to the upper end of its hoist-metering range meters fluid first only from the-'small-capacity pump gradually and progressively to the hoist cylinder until the hoist cylinder is utilizing the full flow capacity of the small pump. When this occurs, the valve begins to meter flow from the large-capacity pump and add it to the full flow of the small pump at an ever-increasing rate until the full flow capacities of both pumps are utilized.

This is shown graphically in FIG. 2, where the vertical line represents flow rate in, gallons per minute, which can be translated in terms of lift speed. The-horizontal line represents spool stroke through the hoistmetering range of the valve spool 36 from its neutral position N to the upper end of its hoist-metering range H. The distance represented by A plus B along the horizontal line is the full spool stroke through its metering range. However, the beginning portion A of the stroke represents that portion of the stroke through which only the flow from the small-capacity pump 26 is metered into the system. Whenthe full capacity of the small pump is utilized, a flow rate is achieved as represented by the point X on the graph. Further stroking of the spool through the upper portion B of its metering range beyond portion A causes spool 36 to gradually meter flow from the large pump into the system in additive relation to the full flow X of the small pump. Finally, at the upper end H of the metering range of the spool, a flow rate Y is produced, which is the full flow capacity of the large pump added to the full flow capacity of the small pump. This represents the full flow capacity of the hydraulic system. Assuming that the tilt and other auxiliary functions are not being utilized, point Y represents the top lift speed of the hoist cylinder.

From the graph it will be apparent that during the stroking of the spool 36 from minimum to maximum, the lift speed or increase in flow rate willproceed in almost a straight-line relationship as represented by the lines L-l and L-2. This characteristic is indicative of a smooth increase or decrease range or spool stroke. This results in smooth operation of the hoist and enables the operator to have excellent control over lift speeds. Small changes in spool stroke in the lower end of the metering range enable the operator to achieve precise inching control and thus small incremental changes in load position at slow speeds.

Hoist-Lowering Mode In FIG. 6 the circuit is in condition for lowering the hoist cylinder and simultaneously,extending the tilt cylinders. Thus tilt spool 34 is stroked inwardly to its tilt E position, whereas hoist spool 36 is stroked inwardly to its L" position. In this mode of operation the flow capacity of the large pump is not needed at all, so its entire flow is diverted through line 58, chambers 59, and 61 of the hoist valve, line 62 and return line 56 to reservoir so that the large pump imposes no appreciable load on the electric motor. Flow from small pump 26, however, is through primary feed line 46 and an upper portion of line 64, through check valve 78 in line 79 to tilt valve chamber 80. From there flow is through line 94 into tilt valve chamber 96, across tilt valve groove 98 into tilt valve chamber 97 and into a line 99 supplying the lower ends of the tilt cylinders 14. Fluid from the opposite ends of the tilt cylinders is exhausted through line 100 into tilt valve chamber 102 and through an internal passage in tilt valve spool 34 represented by openings 103 discharging fluid into tilt valve chamber 104. From there return flow is to line 105 and to return line 56 leading to reservoir 44. Flow through the internal passage is allowed only when a positive pressure exists on the inlet side in cavities 47, 80 and 96 to prevent cavitation in the lower section of tilt cylinders when the load is pulling such cylinders out faster than oil can be supplied.

At the same time, exhaust fluid from hoist cylinder 20 exhausted under the load weight proceeds through line 71, hoist valve chamber 70, across hoist valve spool groove 107, and into hoist valve chamber 108 to line 109 and finally to return line 56 back to reservoir. If desired, a lowering control valve (not shown) could be inserted in line 71 to provide free flow into hoist cylinder 20 but to provide a restricted flow out of such cylinder. Such a valve would prevent excessive lowering speeds or free fall if line 71 should rupture.

Of course, under the condition of the circuit as shown in FIG. 6, if the full flow capacity of small pump 26 is not needed to operate the tilt cylinders and any other auxiliary functions, the additional oil is routed through notches 130 in tilt valve land 131 to cavity 49, line 50, cavities 51, 53 and line 54 to line 56 to tank.

Tilt Mode With the circuit shown, the tilt spool can be positioned to operate the tilt cylinders in any desired mode, regardless of the positioning of the hoist spool. Conversely, the hoist spool can be stroked to operate the hoist cylinder in any desired manner regardless of the positioning of the tilt spool. If the tilt spool is positioned for operating the tilt cylinders at the same time that the hoist spool is stroked to its full-open or high-speed position H, only the speed of operation of the various cylinders is affected.

Thus, for example, in FIG. 5, if the hoist spool is positioned as shown in its full-open, high hoist speed position H, but tilt spool 34 is at position R to retract tilt cylinders 14, the flow from pumps 26 and 28 through the hoist valve to the hoist cylinder 20 would be exactly as described previously with respect to FIG. 5. However, at the same time a portion of the flow from both pumps would be diverted through check valve 78 and line 79 into tilt valve chamber 80. This flow would then proceed across land 112 of tilt spool 34 and into valve chamber 102, and from there through line into the upper ends of tilt cylinders 14. Exhaust fluid from the opposite side of the tilt cylinders would then be forced through line 99, tilt valve chambers 97 and 114, and across spool groove 98 into a line 116 leading to return line 56 and back to reservoir. It should be noted that routing of flow in this case will be strictly a matter of pressure requirement. If the hoist cylinder pressure requirement is lower than the tilt cylinder pressure requirement, all of the flow will go to the hoist cylinder and none to the tilt cylinders. If tilt pressure is lower, enough oil will go to tilt to raise tilt pressure to what is required at the hoist cylinder. This will happen due to the high restriction in the tilt circuit.

Another component of the circuit not previously described is a block representation of an optional auxiliary valve to provide additional control functions for optional attachments and designated 118 in line 54 of FIG. 3.

Having illustrated and described what is presently a preferred embodiment of the invention, it should be apparent to those skilled in the art that the same permits of modification in arrangement and detail. I claim as my invention all such modifications as come within the true spirit and scope of the following claims.

I claim: 1. In an electric motor-operated vehicle, a hydraulic system comprising:

electric motor-driven hydraulic pump means including a small capacity pump and a large capacity P p hydraulic motor means adapted to be driven by hydraulic pressure fluid supplied by said small and large capacity pumps, metering valve means in said system for metering the flow of said pressure fluid from said small and large capacity pumps to said hydraulic motor means,

said metering valve means being movable from a neutral position preventing flow from said small and large capacity pumps to said hydraulic motor means to a full open position directing the full flow capacity of both said small and large capacity pumps through said valve means to said motor means,

said valve means being operable when moved progressively between said neutral and full open positions to meter flow first from said small capacity pump in a manner so as to progressively increase flow therefrom to said motor means from a minimum to the maximum flow capacity of said small pump and then from said large capacity pump in additive relation to the maximum flow of said small capacity pump in a manner so as to progressively increase the flow from said large pump to said motor means from a minimum to the maximum flow capacity of said large pump,

whereby to produce a progressive increase in flow availability to said motor means from a minimum from said small pump to the maximum flow capacity of both said pumps.

2. A system according to claim 1 wherein said metering valve means comprises a single spool valve.

3. A system according to claim 1 wherein movement of said metering valve means is manually controlled.

4. A system according to claim 1 wherein said metering valve means comprises a single manually operated spool valve. n

5. A system according to claim 1 including closed hydraulic fluid reservoir means for housing a supply of said hydraulic pressure fluid, said small and large capacity pumps being enclosed within said reservoir means.

6. A system according to claim 1 wherein said vehicle comprises a battery-powered electric lift truck and said hydraulic motor means comprises a hydraulic-powered extensible cylinder means.

7. A system according to claim 6 wherein said cylinder means comprises a hoist cylinder for said lift truck.

8. A system according to claim 1 wherein said small and large capacity pumps are driven by the same constant speed electric motor.

9. A system according to claim 8 wherein said large and small capacity pumps are driven at a constant speed and have fixed displacements.

10. A system according to claim 1 wherein said hydraulic motor means includes multiple hydraulic motor means each for operating a different function of said vehicle, said metering valve means being interposed between said pumps and only one of said multiple motor means.

11. A system according to claim 1 including a common hydraulic fluid reservoir for said small and large capacity pumps, said reservoir enclosing both said pumps and said metering valve means in a manner so that any hydraulic fluid leakage from said pumps or valve means is retained within said reservoir.

12. A system according to claim 1 wherein said vehicle comprises a battery-operated electric lift truck and said hydraulic motor means includes a hoist cylinder means and a tilt cylinder means, said small and large capacity pumps supplying pressure fluid to both said tilt cylinder means and said hoist cylinder means, a first valve for controlling flow to said tilt cylinder means, said metering valve means including a second valve for metering flow to said hoist cylinder means, and a common valve block housing both said first and second valves, said pump means including a hydraulic fluid res ervoir housing both said small-capacity pump and said large-capacity pump and also housing said valve block.

13. A system according to claim 1 wherein said metering valve means includes a single multiple position spool valve selectively movable between (a) a first neutral position preventing the operation of said motor means, (b) a second position for operating said hydraulic motor means in one direction and (c) a third metering range of positions for operating said hydraulic motor means in the opposite direction at varying speeds depending on the position of said valve spool within said metering range.

14. A system according to claim I wherein said hydraulic motor means comprises a hydraulic cylinder and said metering valve means comprises a single valve spool movable between (a) a first position blocking flow to and from said cylinder, (b) a second position for retracting said cylinder and (c) a third metering range of positions for extending said cylinder at variable speeds by metering flow to said cylinder, said spool being movable from a low end of said metering range to the upper end thereof so as to effect a progressively increasing flow of pressure fluid to said cylinder first increasingly from said small capacity pump only until said small capacity pump reaches its maximum flow capacity and then from said small capacity pump under maximum flow and in addition from said large capacity pump under progressively increasing flow until the maximum flow capacities of both said pumps is reached.

15. In a hydraulic control system for controlling the operation of a hydraulic motor means,

at least two pumps in said system for supplying pressure fluid for operating said motor means,

hydraulic circuit means for circulating pressure fluid in said system including a circuit portion interconnecting said pumps and said motor means, and a single metering valve interposed in said circuit portion for controlling the flow of pressure fluid between said two pumps and said motor means,

said metering valve being movable through a metering range and being operable when stroked from the lower to the upper end of said range to meter flow at a progressively increasing rate to said motor means,

said metering valve and circuit being interrelated and operable together within the pressure limitations of said circuit in a manner such that as said metering valve is stroked from the lower end to the upper end of said metering range flow ismetered first only one of said two pumps to said motor means at a progressively increasing rate until the full flow capacity of said one pump is consumed by said motor means, and then flow is metered from the other of said two pumps to said motor means at a progressively increasing rate while the full flow capacity of said one pump continues to said motor means, until the full flow capacities of both pumps are consumed by said motor means.

16. A hydraulic control system according to claim 15 wherein said motor means comprises multiple hydraulic motor means in said circuit means for operating multiple hydraulic functions and a separate control valve in said circuit means for controlling the operation of each separate function, the operation of said metering valve as described being unaffected by the simultaneous operation of any of said separate control valves.

17. A system according to claim 15 wherein said pumps are driven by a common motor means.

18. A system according to claim 15 wherein said pumps are driven by a common constant speed motor means.

19. A hydraulic control system for operating the load-handling functions of a battery-powered electric lift truck, said system comprising:

a constant-speed electric motor powered by the battery power system of said truck,

said electric motor driving a small capacity pump and a large capacity pump,

said hydraulic control system including a hydraulic control circuit supplied with pressure fluid by said pumps and including a pressure fluid reservoir,

multiple hydraulic motor means in said circuit including a hoist motor means and a tilt motor means,

a manually-operated tilt valve in said circuit between said pumps and said tilt motor means for controlling the operation of said tilt motor means,

a manually-operated hoist valve in said circuit between said pumps and said hoist motor means for controlling the operation of said hoist motor means, said circuit being operable in a first neutral position and in a second hoist-lowering position of said hoist valve to recirculate substantially all flow from said large capacity pump to said reservoir while said flow bypasses said hoist and tilt motor means irrespective of the operating position of said tilt valve, said circuit being operable in a third hoistelevating range of positions of said hoist valve to meter flow from said small and large capacity pumps in a manner such that as said hoist valve is stroked from the low end to the high end of its metering range, flow is metered first only from said small capacity pump at a progressively increasing rate to said hoist motor means until the full capacity of said small pump is utilized and then flow is metered from said large capacity pump to said hoist motor means at a progressively increasing rate in additive relation to the full flow from said small capacity pump until the full flow capacities of both pumps are utilized, said tilt and hoist valves coacting in a manner such that when said tilt valve is in a tilt motor-operating position and said hoist valve is stroked through its hoist-elevating range, flow is metered progressively first from said small capacity pump and then from both said small and large capacity pumps as aforesaid to both said tilt and hoist motor means. 20. A hydraulic control system according to claim 19 wherein said tilt and hoist-metering valves include single valve spools housed within a common valve block,

said valve block and said small and large capacity pumps being enclosed within said fluid reservoir.

21. A hydraulic control system according to claim 19 wherein said tilt and hoist valves when both are in their respective motor-operating positions are connected in said hydraulic control circuit and said circuit operates in a manner such that (a) when the pressure requirement at said hoist motor means is lower than the pressure requirement at said tilt motor means, all available flow is routed to said hoist motor means and such that (b) when the pressure requirement at said tilt motor means is lower than the pressure requirement at said hoist motor means, only a sufiicient portion of the available flow is routed to said tilt motor means to raise the inlet pressure at said tilt motor means to the required pressure at said hoist motor means.

22. A hydraulic control system according to claim 21 wherein said tilt valve comprises a tilt valve spool slidable within a valve cavity including a cavity portion operable as part of a fluid return passage means for directing exhaust fluid from said tilt motor means back to said reservoir when said spool is positioned for operating said tilt motor means, said spool including flowrestricting means operable when said spool is positioned for tilting a mast of said lift truck forwardly to restrict return flow from said tilt motor means through said cavity portion and thereby prevent cavitation at said tilt motor means when a load tends to drive said tilt motor means as a pump, said flow-restricting means being inactive in the other positions of said spool. 

1. In an electric motor-operated vehicle, a hydraulic system comprising: electric motor-driven hydraulic pump means including a small capacity pump and a large capacity pump, hydraulic motor means adapted to be driven by hydraulic pressure fluid supplied by said small and large capacity pumps, metering valve means in said system for metering the flow of said pressure fluid from said small and large capacity pumps to said hydraulic motor means, said metering valve means being movable from a neutral position preventing flow from said small and large capacity pumps to said hydraulic motor means to a full open position directing the full flow capacity of both said small anD large capacity pumps through said valve means to said motor means, said valve means being operable when moved progressively between said neutral and full open positions to meter flow first from said small capacity pump in a manner so as to progressively increase flow therefrom to said motor means from a minimum to the maximum flow capacity of said small pump and then from said large capacity pump in additive relation to the maximum flow of said small capacity pump in a manner so as to progressively increase the flow from said large pump to said motor means from a minimum to the maximum flow capacity of said large pump, whereby to produce a progressive increase in flow availability to said motor means from a minimum from said small pump to the maximum flow capacity of both said pumps.
 2. A system according to claim 1 wherein said metering valve means comprises a single spool valve.
 3. A system according to claim 1 wherein movement of said metering valve means is manually controlled.
 4. A system according to claim 1 wherein said metering valve means comprises a single manually operated spool valve.
 5. A system according to claim 1 including closed hydraulic fluid reservoir means for housing a supply of said hydraulic pressure fluid, said small and large capacity pumps being enclosed within said reservoir means.
 6. A system according to claim 1 wherein said vehicle comprises a battery-powered electric lift truck and said hydraulic motor means comprises a hydraulic-powered extensible cylinder means.
 7. A system according to claim 6 wherein said cylinder means comprises a hoist cylinder for said lift truck.
 8. A system according to claim 1 wherein said small and large capacity pumps are driven by the same constant speed electric motor.
 9. A system according to claim 8 wherein said large and small capacity pumps are driven at a constant speed and have fixed displacements.
 10. A system according to claim 1 wherein said hydraulic motor means includes multiple hydraulic motor means each for operating a different function of said vehicle, said metering valve means being interposed between said pumps and only one of said multiple motor means.
 11. A system according to claim 1 including a common hydraulic fluid reservoir for said small and large capacity pumps, said reservoir enclosing both said pumps and said metering valve means in a manner so that any hydraulic fluid leakage from said pumps or valve means is retained within said reservoir.
 12. A system according to claim 1 wherein said vehicle comprises a battery-operated electric lift truck and said hydraulic motor means includes a hoist cylinder means and a tilt cylinder means, said small and large capacity pumps supplying pressure fluid to both said tilt cylinder means and said hoist cylinder means, a first valve for controlling flow to said tilt cylinder means, said metering valve means including a second valve for metering flow to said hoist cylinder means, and a common valve block housing both said first and second valves, said pump means including a hydraulic fluid reservoir housing both said small-capacity pump and said large-capacity pump and also housing said valve block.
 13. A system according to claim 1 wherein said metering valve means includes a single multiple position spool valve selectively movable between (a) a first neutral position preventing the operation of said motor means, (b) a second position for operating said hydraulic motor means in one direction and (c) a third metering range of positions for operating said hydraulic motor means in the opposite direction at varying speeds depending on the position of said valve spool within said metering range.
 14. A system according to claim 1 wherein said hydraulic motor means comprises a hydraulic cylinder and said metering valve means comprises a single valve spool movable between (a) a first position blocking flow to and from said cylinder, (b) a second position for retracting said cylinder and (c) a third metering range of positions for extending said cylinder at variable speeds by metering flow to said cylinder, said spool being movable from a low end of said metering range to the upper end thereof so as to effect a progressively increasing flow of pressure fluid to said cylinder first increasingly from said small capacity pump only until said small capacity pump reaches its maximum flow capacity and then from said small capacity pump under maximum flow and in addition from said large capacity pump under progressively increasing flow until the maximum flow capacities of both said pumps is reached.
 15. In a hydraulic control system for controlling the operation of a hydraulic motor means, at least two pumps in said system for supplying pressure fluid for operating said motor means, hydraulic circuit means for circulating pressure fluid in said system including a circuit portion interconnecting said pumps and said motor means, and a single metering valve interposed in said circuit portion for controlling the flow of pressure fluid between said two pumps and said motor means, said metering valve being movable through a metering range and being operable when stroked from the lower to the upper end of said range to meter flow at a progressively increasing rate to said motor means, said metering valve and circuit being interrelated and operable together within the pressure limitations of said circuit in a manner such that as said metering valve is stroked from the lower end to the upper end of said metering range flow is metered first only one of said two pumps to said motor means at a progressively increasing rate until the full flow capacity of said one pump is consumed by said motor means, and then flow is metered from the other of said two pumps to said motor means at a progressively increasing rate while the full flow capacity of said one pump continues to said motor means, until the full flow capacities of both pumps are consumed by said motor means.
 16. A hydraulic control system according to claim 15 wherein said motor means comprises multiple hydraulic motor means in said circuit means for operating multiple hydraulic functions and a separate control valve in said circuit means for controlling the operation of each separate function, the operation of said metering valve as described being unaffected by the simultaneous operation of any of said separate control valves.
 17. A system according to claim 15 wherein said pumps are driven by a common motor means.
 18. A system according to claim 15 wherein said pumps are driven by a common constant speed motor means.
 19. A hydraulic control system for operating the load-handling functions of a battery-powered electric lift truck, said system comprising: a constant-speed electric motor powered by the battery power system of said truck, said electric motor driving a small capacity pump and a large capacity pump, said hydraulic control system including a hydraulic control circuit supplied with pressure fluid by said pumps and including a pressure fluid reservoir, multiple hydraulic motor means in said circuit including a hoist motor means and a tilt motor means, a manually-operated tilt valve in said circuit between said pumps and said tilt motor means for controlling the operation of said tilt motor means, a manually-operated hoist valve in said circuit between said pumps and said hoist motor means for controlling the operation of said hoist motor means, said circuit being operable in a first neutral position and in a second hoist-lowering position of said hoist valve to recirculate substantially all flow from said large capacity pump to said reservoir while said flow bypasses said hoist and tilt motor means irrespective of the operating position of said tilt valve, said circuit being operable in a third hoist-elevating range of positions of said hoist valve to meter flow from said small and large capacity pumps in a manner such that as said hoist vAlve is stroked from the low end to the high end of its metering range, flow is metered first only from said small capacity pump at a progressively increasing rate to said hoist motor means until the full capacity of said small pump is utilized and then flow is metered from said large capacity pump to said hoist motor means at a progressively increasing rate in additive relation to the full flow from said small capacity pump until the full flow capacities of both pumps are utilized, said tilt and hoist valves coacting in a manner such that when said tilt valve is in a tilt motor-operating position and said hoist valve is stroked through its hoist-elevating range, flow is metered progressively first from said small capacity pump and then from both said small and large capacity pumps as aforesaid to both said tilt and hoist motor means.
 20. A hydraulic control system according to claim 19 wherein said tilt and hoist-metering valves include single valve spools housed within a common valve block, said valve block and said small and large capacity pumps being enclosed within said fluid reservoir.
 21. A hydraulic control system according to claim 19 wherein said tilt and hoist valves when both are in their respective motor-operating positions are connected in said hydraulic control circuit and said circuit operates in a manner such that (a) when the pressure requirement at said hoist motor means is lower than the pressure requirement at said tilt motor means, all available flow is routed to said hoist motor means and such that (b) when the pressure requirement at said tilt motor means is lower than the pressure requirement at said hoist motor means, only a sufficient portion of the available flow is routed to said tilt motor means to raise the inlet pressure at said tilt motor means to the required pressure at said hoist motor means.
 22. A hydraulic control system according to claim 21 wherein said tilt valve comprises a tilt valve spool slidable within a valve cavity including a cavity portion operable as part of a fluid return passage means for directing exhaust fluid from said tilt motor means back to said reservoir when said spool is positioned for operating said tilt motor means, said spool including flow-restricting means operable when said spool is positioned for tilting a mast of said lift truck forwardly to restrict return flow from said tilt motor means through said cavity portion and thereby prevent cavitation at said tilt motor means when a load tends to drive said tilt motor means as a pump, said flow-restricting means being inactive in the other positions of said spool. 